1. Technical Field
The present disclosure relates to a method for designing freeform surface off-axial imaging system with a real exit pupil based on point-by-point construction and iteration process.
2. Description of Related Art
In infrared imaging system, in order to increase the signal-to-noise ratio and the sensitivity of the system, the cooled detector and cold stop are used, especially the cold stop is located near the exit pupil. Thus, the infrared imaging system often has a real exit pupil at the position in front of the image surface. Furthermore, the infrared imaging system often uses an off-axial imaging system to reduce the transmission loss and eliminate the central obscuration. Thus, it is hard to design.
In recent years, with the development of the advancing manufacture technologies, freeform surfaces have been successfully used in the optical field, such as head-mounted-displays, reflective systems, varifocal panoramic optical systems, and micro-lens arrays. The freeform surface is used in the infrared imaging system. However, in conventional direct design methods, the freeform surfaces are designed by a direct construction method, it is hard to form a real exit pupil with small distortion, and further optimization will be much more difficult.